Magnetic Resonance Imaging (MRI)
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Magnetic resonance imaging (MRI) is the clinically preferred method for imaging soft tissue because it can produce a clearer, more detailed view of internal organs than computed tomography (CT) without the radiation exposure associated with CT. In certain areas of the body, such as the abdomen, pelvis and breast, MRI allows doctors to more easily differentiate a tumor or tumor bed from healthy tissue, which can be difficult to differentiate on CT. For example, MRI-guided radiation therapy is superior to CT-guided therapy in differentiating lumpectomy cavities after surgery for breast cancer. The clearer visualization potentially allows for more precise therapy by reducing treatment margins and limiting radiation-induced tissue scarring.
This content originally appeared online at UCLA Health.
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Men who have been treated for prostate cancer, even with only hormones, must be aware that hormone and radiation therapy can change the prostate magnetic resonance imaging (MRI) appearance. The entire gland appears normal; asymmetry and subtlety become more important in identifying suspect areas. Therefore, it’s important that the radiologist be informed if there was any prior treatment.
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People with incompatible pacemakers or hardware may need to do detailed screenings to get an MRI.
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The only way to see inside a human body better that with an MRI is to cut it open. MRIs are ideal for:
- Visualizing shoulder injuries
- Diagnosing multiple sclerosis
- Diagnosing infections in the brain, spine or joints
- Diagnosing tendonitis
- Visualizing torn ligaments in the wrist, knee and ankle
- Evaluating masses in the body's soft tissues
- Diagnosing strokes in their earliest stages
- Evaluating bone tumors, cysts and bulging or herniated discs
- Diagnosing tumors of the pituitary gland and brain
These are only a few of many reasons to perform an MRI scan.
MRI systems do not use ionizing radiation, which is a comfort to many patients. Advantages to the system also include the fact that MRI contrast materials (dyes) have a very low incidence of side effects. MRIs also have the ability to take images in any plane. CT scans are limited to one plane, the axial plane (If you think of a loaf-of-bread, the axial plane is how the loaf is sliced normally). An MRI system can make axial images as well as images in a sagitall plane (as if it were slicing bread lengthwise) and coronally (like the layers of a cake) or, for that matter, any degree in between. It can do all of this without the patient having to move.
If you've ever had an X-ray, you know that you have to move every time they take a different picture.
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The process of magnetic resonance imaging (MRI) can be explained as:
- Nuclei of the molecules within a human body are randomly aligned magnetically.
- When we walk into a room with a strong magnetic field, those same molecules align themselves to the magnetic field.
- For an MRI examination, a coil placed on or around you generates a pulse of energy.
- The molecules then realign with the pulse of energy.
- When the pulse is turned off or reapplied, the molecules return to their positions, creating a detectable signal.
- These detectable signals are processed by the computer into a series of images.
- Patients feel no pain during the MRI examination.
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Magnetic resonance imaging (MRI) machines usually are located at hospitals or special medical imaging facilities. A radiologist (ra-de-OL-o-jist) or other doctor who has special training in medical imaging oversees MRI testing. Cardiac MRI usually takes 45 to 90 minutes, depending on how many pictures are needed. The test may take less time with some newer MRI machines. The MRI machine will be located in a specially constructed room. This will prevent radio waves from disrupting the machine. It also will prevent the MRI machine's strong magnetic fields from interfering with other equipment.
Traditional MRI machines look like a long, narrow tunnel. Newer MRI machines, called short-bore systems, are shorter, wider and don't completely surround you. Some of the newer machines are open on all sides. Your doctor will help decide which type of machine is best for you. Cardiac MRI is painless and harmless. You'll lie on your back on a sliding table that goes inside the tunnel-like machine.
You will need to remain very still during the test. Any movement may blur the pictures. If you're unable to lie still, you may be given medicine to help you relax. You may be asked to hold your breath for 10 to 15 seconds at a time while the technician takes pictures of your heart.
A contrast agent, such as gadolinium (gad-oh-LIN-e-um), may be used to highlight your blood vessels or heart in the pictures. Contrast agent usually is injected into a vein in your arm with a needle. You may feel a cool sensation during the injection and discomfort where the needle was inserted. Gadolinium doesn't contain iodine, so it won't cause problems for people who are allergic to iodine.
Your cardiac MRI may include a stress test to detect blockages in your coronary arteries. If so, you'll get other medicines to increase the blood flow in your heart or to increase your heart rate.
This answer from the National Heart, Lung and Blood Institute has been reviewed and/or edited by Dr. William D. Knopf.
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MRI (magnetic resonance imaging) uses radio waves and strong magnets to create images of your body tissues. Many images are created during an MRI test, each focused on a different plane or "slice" of your heart. A computer combines them to create detailed pictures or movies of your heart.
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MRI scans are ideal for diagnosing and evaluating many conditions, but they do have drawbacks. For example:
- Many people cannot be scanned safely with MRI (i.e., because they have pacemakers). Also, some people are too big to be scanned.
- Many people are claustrophobic. For them, being in an MRI machine can be very disconcerting.
- The MRI machine makes a tremendous amount of noise. The noise sounds like a continual, rapid hammering. Patients can be given earplugs or stereo headphones in an attempt to muffle the noise. The noise is from the rising electrical current in the gradient magnets' wires as it is being opposed by the main magnetic field.
- Patients must remain very still for extended periods of time when getting an MRI scan. The exams can range from 20 minutes to 90 minutes, sometimes more. Even very slight movement can cause distorted images that will have to be repeated.
- If the area of the scan has orthopedic hardware (such as screws, plates or artificial joints) the image can have severe distortions. This hardware causes a significant alteration in the magnetic field and a uniform field is critical to good imaging.
- MRI machines are very expensive; therefore the exams are also very expensive.
Despite these drawbacks, MRIs offer almost limitless benefits.
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During the magnetic resonance imaging (MRI) examination, which takes an average of 30 minutes, a "knocking" sound can be heard. This is a normal effect of the gradient coils responding to the different fields. Despite this noise, most patients can easily tolerate the procedure. A technologist is always in close observation and intercom communication with the patient throughout the procedure.
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A cardiac MRI (cMRI) is a scan that provides pictures of the heart and blood vessels inside the body using a magnetic field and pulses of radio wave energy. Unlike a CT scan, it does not use x-ray radiation. The cMRI generates images of the heart and blood vessels, which can help your doctor assess the heart’s structure and function. In addition to providing information on anatomy, cardiac MRI can also provide information on blood flow through the heart and vessels, function of heart valves, blood supply to the heart muscle and if scars have formed within the heart muscle. Some kinds of stress testing can be performed with a cMRI as well. A cMRI scan takes longer to perform than a cardiac CT scan.
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